1. Field of the Invention
The present invention relates to a method and system for radio data communication, etc., whereby circuit-switched communication and packet-switched communication are intermingled according to a TDMA mode.
2. Related Art
First, characteristics of the circuit-switched communication and the packet-switched communication will be briefly explained below. When a circuit-switched communication is carried out between a radio base station and a radio terminal, a radio link is established using a radio channel and the link continues to be held whether there is data to be sent or received or not. Therefore, the circuit-switched communication is not suitable to effectively use the radio channel although it is always possible to send and receive data without delay while the radio link is held.
On the other hand, in the packet-switched communication, a radio link is only established at a necessary period (when sending and receiving data) and the radio link never continues wastefully to be held. In the packet-switched communication, data is transmitted in the form of a packet (dividing into a constant capacity unit) with adding an address of a receiving side to the data, and during the communication, it is not necessary to always hold the radio link. Therefore, radio channel resources can be effectively used in the packet-switched communication. However, a delay occurs necessarily to use an idle radio channel.
FIG. 5 is a timing chart to explain a communication method to execute a data communication call in a circuit switching form (circuit-switched data) and a data communication call in a packet switching form (packet-switched data) simultaneously by TDMA (Time Division Multiple Access) using a conventional four-slot-structure. In FIG. 5, one in four slots is used for a control channel, and the repetition period of this control channel is set every three TDMA frames. In this figure, the abscissa axis shows elapsed time, and first TDMA slot group 1--fourth TDMA slot group 14 are arranged lengthwise. Also, each cell represents one of the TDMA slots, and while a hatched or dotted cell is a used slot, a plain cell is an idle slot. Here, the first TDMA slot group 11 is used as a control channel 15, and a repetition period of control channel 15 is set every three TDMA frames as mentioned above. Also, the second TDMA slot group 12 is already used for circuit-switched data.
A new circuit-switched data is generated at time point A in FIG. 5. There, the use of the third TDMA slot group 13 is begun corresponding to the generated data. Moreover, a packet-switched data originates at point B. Corresponding to that, the fourth TDMA slot group 14 is begun to use halfway. The use of the first TDMA slot group 11 of the control channel after this is repeated every three TDMA periods. However, the second TDMA slot group 12 to the fourth TDMA slot group 14 are changed to a condition having an idle slot being accompanied by ending of the circuit-switched data or the packet-switched data (e.g., at point C). In this way, a TDMA slot group having an idle slot is begun to be used when a new call is generated in a communication method shown in FIG. 5.
FIG. 6 is a timing chart that explains a case where a circuit-switched data becomes a call-loss because there is no idle slot in a conventional data communication method. In FIG. 6, the first TDMA slot group 11 is used for control channel 15, and the second TDMA slot group 12 and the third TDMA slot group 13 are already used for circuit-switched data. In FIG. 6, a packet-switched data 21 originates at point D. Then, the fourth TDMA slot group 14 that has an idle slot is begun to be used at the point correspondingly to it. If a circuit-switched data 22 is generated at point E immediately after origination of data 21, because there is no idle slot in the fourth TDMA slot group 14, a call-loss originates at point E. Moreover, in FIG. 6, immediately after this, the use of packet-switched data 21 ends by point F and the fourth TDMA slot group 14 changes to have an idle slot. In this way, FIG. 6 shows an example wherein the circuit-switched data 22 has a call-loss due to the small little time difference between the origination of packet-switched data 21 and the origination of circuit-switched data 22.
Here, it is supposed that circuit-switched data 22 originates earlier than packet-switched data 21. In this case, as may be understood from FIG. 5 or FIG. 6, generally, the time of use for the circuit-switched data is longer than that for the packet-switched data. Therefore, not only long stand-by time until transmission of this packet-switched data 21, but also call-loss when the stand-by time exceeds the permitted delay time, results caused. As mentioned above, a circuit-switched data in TDMA data communication immediately becomes a call-loss if there is no idle slot when it is generated. Because a TDMA slot group is used continuously while a radio link is held, even if there is no significant data on the way, the slot use time becomes comparatively long. Therefore, the packet-switched data may have to wait for a long time until an idle slot originates, even if the packet length is short, and this is not efficient.